I'm A Runner And Have Developed Left Lateral Mid Foot

I'm a runner and have developed left lateral mid foot soft tissue swelling. No pain only when pressure is placed on the outer knife surface of the foot. Swelling of soft tissue is evident in that area radio graphically and there is a lateral bone inclusion that is round with similar bone density to the surrounding bone. I'm training for Boston marathon and have had metatarsal stress fractures of both feet in the past. This doesn't have a stress fracture appearance and is a dull ache as if bruised. The lesion is on the lateral bone surface with no lysis. Any thoughts?
Thank you
Michele